Electrical connections have, until recently, largely depended upon traditional methods such as soldering and crimping to effect the connection of, for example, conductors and cable screens. Widely used connection methods also have included pin and socket connectors as well as nut and bolt connectors.
In particular applications, it is necessary to employ reusable devices. While traditional pin and socket devices are generally considered to be reusable, the strength of the resulting physical and electrical connection is not sufficient for many applications. A soldered connection typically provides sufficient electrical continuity, however it is often not reusable because of its physical location or the heat sensitivity of closely proximate components. Additionally, a soldered connection may break down as a result of the operating conditions encountered in particular applications. Nut and bolt connections can come loose and are difficult to use in close quarters. While crimping devices generally have sufficient physical strength, they too are not generally reusable. Therefore, there is a recognized need for a reusable connecting device which can provide high electrical conductivity as well as a strong physical connection with another object, especially in environments over 200.degree. C. and under high vibration conditions.
Recently, heat recoverable metals have been used in reusable connecting devices such as those disclosed in U.S. Pat. Nos. 4,022,519 ('519) and 3,740,839 ('839) the disclosures of which are both incorporated herein by reference. As set forth in '519 and '839, heat recoverable metals are usable for connecting devices. Basically, these heat recoverable metals are alloys which exhibit the shape memory effect. An article made from heat recoverable metal can be reversibly deformed after being cooled to near or below its martensitic transition temperature M.sub.s (the temperature at which transformation begins). If the metal is so deformed and subsequently warmed above its austenitic transition temperature A.sub.s (the temperature at which the metal starts to revert back to austenite) the heat recoverable metal recovers toward its original configuration. The recovery ends at A.sub.f (the temperature at which the transition to austenite is complete).
The device of '839 is a reusable connecting device which utilizes a heat recoverable metallic band disposed about a resilient member, such as the tines of a forked member. The tines are spaced from one another so that they can be moved inwardly, but when so moved, exert an outward force. When it is desired to make a connection between the device and other objects, the band is warmed to a temperature sufficient to cause the metal to transform to its austenitic phase. The band then shrinks with a force sufficient to overcome the opposing force of the tines, such that the tines are moved inwardly, toward one another to contact and hold an object between them. The device is reusable in that when the temperature of the band is lowered sufficiently to cause the metal to transform to its martensitic phase, the opposing force of the tines overcomes the yield strength of the band, thereby outwardly expanding the band and allowing the object placed between the tines to be released.
The device of '519 also discloses a reusable connector. The connector includes a heat recoverable metallic band disposed about a non-resilient, deformable member, typically a hollow cylinder that has been slotted to form tines. When it is desired to make a connection between the device and other objects, the band is lowered to a temperature sufficient to cause the metal to transform to its martensitic phase. The object is inserted between the tines, forcing the tines and consequently the band in its martensitic phase to be expanded outwardly. To secure the connection, the band is warmed to a temperature sufficient to cause the metal to transform to its austenitic phase. The band contracts and drives the tines towards their original configuration, thereby engaging the object. The connector is reusable in that upon lowering the temperature of the band sufficient to cause a martensitic phase transformation of the metal, the band relaxes sufficiently to allow the object to be removed from the connector by deforming the deformable member.
The device of the instant invention, unlike the devices of '519 and '839, is capable of creating a contact force with a substrate regardless of the temperature and hence phase of the heat recoverable metal, sufficient to provide a physical connection and preferred electrical continuity to the connection. The instant invention accomplishes the above through the use of resiliently deformable tines which grip a substrate with sufficient force to provide a physical connection which in the case of conductive tines provides electrical continuity, regardless of the temperature and hence phase of a heat recoverable metal band defining a driver member which surrounds the tines. However, at the A.sub.s temperature, the driver member begins to contract and above the A.sub.f temperature it has contracted sufficiently to supplement the force of the tines against the substrate.